The present invention relates to material handling vehicles and, more specifically, to extendable mast systems and methods for material handling vehicles.
Vertically extendable mast assemblies are useful on material handling vehicles for the transportation and placement of loads at varying heights. The mast assemblies can include two or more masts, each mast having two flanges and a web. Vertically extendable mast assemblies typically employ a roller bearing arrangement that facilitates vertical translation of an extendable mast with respect to an already extended mast or a fixed base. In some cases, the bearing can be angularly positioned (canted bearing) such that the bearing contacts the web and one of the flanges that acts as the load bearing flange. Canted bearings are used to help accommodate for variations in parallelism in the vertically extendable mast sections.
A torsional load can be placed on the extendable mast or the fixed base that is caused by twisting or tolerance variations in the structure of at least one of the fixed base or extendable mast. The torsional load may cause variations in position and angle of the first and second flange of the fixed base or extendable mast. Variations in position and angle of the first and second flange may be greatest between a bottom end and a top end of the fixed base or extendable mast when the mast assembly is in a vertically extended arrangement.
A roller bearing can be used for each mast telescopic interface, and the roller bearing is typically intended to ride on only one flange. At times, there may be little or no clearance between the roller bearing and an opposing, non-load bearing flange. The rotation of the roller bearing is driven through contact with the mast. As the roller bearing is forced to move away from the load bearing flange due to the torsional load, it continues to rotate in the same direction. Once the clearance to the opposite flange is taken up, the roller bearing continues to rotate in the same direction, and can contact the non-load bearing flange.
What is needed is systems and methods to improve extendable masts that account for a torsional load.